The present invention relates to a pressure-limiting valve for limiting the pressure in a return-flow line which extends from an injection system to a sucking-jet pump of a fuel delivery device of a fuel tank, which valve has a closure member which is urged by a closing spring into closed position against a valve seat, said closure member in its open position releasing a pressurized fluid connection from the return-flow line to the fuel tank, bypassing the sucking-jet pump.
Pressure-limiting valves of the above type are used in return-flow lines which extend in a motor vehicle from the injection system back to the fuel tank. In this connection the amount of fuel which flows back is conducted through a sucking-jet pump, in order by means of the latter, to draw, for instance, fuel from the fuel tank into a surge pot from which a fuel pump conveys fuel to the injection system.
Since the amount of fuel which flows back varies as a function of the instantaneous fuel consumption of the motor vehicle, corresponding pressure variations would occur in the return-flow line if a pressure-limiting valve were not used. Such variations in pressure would, however, affect the manner of operation of the sucking-jet pump. It is therefore necessary to limit these variations in pressure. In order to avoid reactions on the pressure regulator of the injection system, the pressure of the return flow must not be greater than about 1.4 bar and must exhibit only slight variations in pressure. In modern motor vehicles, pressure variations of between 1 bar and 1.4 bar can still be tolerated.
It has been found in practice that with ordinary pressure-limiting valves brief variations in pressure of more than 1.4 bar cannot be avoided. This is due to the fact that, after the initial opening of the closure member of the valve, there is a repeated brief closing of the closure member, thus producing pressure surges. The reason for this is that when the closure member is open, eddies form behind the valve seat in the pressure-limiting valve as a result of burbling phenomena, leading to an oscillating of the closure member and thus to pressure pulses.